1. Field of the Invention
The present invention relates to a surface emitting laser and a method of manufacturing the same.
2. Description of the Related Art
In a surface emitting laser, as an effective method for achieving a low threshold current, (1) a method of reducing a loss by increasing reflectivity of a reflecting film and (2) a method of improving current injection efficiency by constricting a region where a current flows so as to make a sectional area of an active layer very small are known. In general, high performance is aimed at by using these methods jointly.
In a method of realizing high reflectivity, a distributed Bragg reflector (DBR) mirrors are provided above and below a cavity, and very high reflectivity is obtainable by this method. The DBR mirror is composed of a semiconductor or dielectric multilayer film.
A following method is known as a typical method of constricting a current.
First, there is a method of burying a very small cavity in a semiconductor layer, which is reported in Technical Digest of 13th IEEE International Semiconductor Laser Conference, Sep. 24, 1992, pp. 212-213. Secondly, there is a method of forming a vertical-cavity having an active layer with a very small area by patterning a semiconductor film, and the techniques thereof are described in Applied Physics Letters, Vol. 57 No. 16, 15 Oct. 1990, pp. 1605-1607. Thirdly, a method of forming a high resistance layer by implanting hydrogen ions into a semiconductor layer around a cavity and surrounding the cavity by the high resistance layer has been reported in Technical Digest of 13th IEEE International Semiconductor Laser Conference, Sep. 24, 1992, pp. 3-4.
When a vertical-cavity is buried into a semiconductor layer, however, such a highly advanced technique that an opening is formed in a semiconductor layer and a cladding layer, an active layer or the like are laminated therein with high controllability is required, thus lowering yield.
Further, it is comparatively easy to form a vertical-cavity of a surface emitting laser through patterning by present dry etching techniques, but the side of the active layer is damaged by etching. As a result, carriers are caught by crystal defects of the side portion of the active layer, and not only the carriers contributing to emission are reduced, but also non-emitting recombination is increased in the active layer, thus resulting in lowering of emission efficiency.
Further, although the effect of current constriction is large in a surface emitting laser having a structure that a cavity is surrounded by a high resistance layer formed by ion implantation, controllability of constriction width is deteriorated by ion implantation, thus causing poor reliability.